This invention relates to a liquid-cooled internal combustion engine, and more particularly it is concerned with sealing means for sealing between a cylinder and a cylinder head of the liquid-cooled internal combustion engine.
In a liquid-cooled internal combustion engine including a cylinder and a cylinder head each provided with an inner shell and an outer shell, the cylinder and the cylinder head being connected to each other to provide cooling liquid chambers defined by the outer shells and the inner shells of the cylinder and the cylinder head while a combustion chamber is formed by the inner shells of the cylinder and the cylinder head, it is necessary that surfaces of contact between the cylinder and cylinder head be sealed to avoid leaking of gas from the combustion chamber and leaking of cooling liquid from the cooling liquid chambers. To this end, sealing means has hitherto been provided between the cylinder and cylinder head, to avoid leaking of gas and cooling liquid. This type of sealing means of the prior art has, however, had the disadvantage that difficulties are encountered in positively avoiding, in particular, the leaking of gas from the combustion chamber, and also had the disadvantage that the production cost of the sealing means itself is high or that the production cost of the cylinder or the cylinder head is increased due to the provision of the sealing means. Also, there has hitherto been the danger that some of the sealing means interfere with normal combustion in the internal combustion engine.
FIGS. 1 to 3 show liquid-cooled internal combustion engines provided with this type of sealing means of the prior art. In order to clarify the aforesaid disadvantages of the prior art, the liquid-cooled internal combustion engines of the prior art will be described by referring to FIGS. 1 to 3.
The liquid-cooled internal combustion engine shown in FIG. 1 comprises a cylinder 1 and a cylinder head 6. The cylinder 1 is provided with an inner shell 3 and an outer shell 5, and the cylinder head 6 is also provided with an inner shell 8 and an outer shell 10. The cylinder head 6 is connected at its lower end surface to the upper end surface of the cylinder 1 through sealing means comprising gasket 14. The inner shells 3 and 8 of the cylinder 1 and cylinder head 6 respectively define a combustion chamber 2, and a portion of the combustion chamber 2 defined by the inner shell 8 of the cylinder head 6 forms an upper combustion chamber 7. Moreover, the inner shells 3 and 8 and the outer shells 5 and 10 of the cylinder 1 and the cylinder head 6 respectively define cooling liquid chambers 4 and 9 communicating with each other.
As shown in FIG. 2, the gasket 14 is formed of an annular asbestos plate 12 which has core bars 11 embedded therein and grommets 13 of stainless steel wound around the inner and outer peripheries thereof. The gasket 14 of this construction is arranged between the end surfaces of the cylinder 1 and cylinder head 6, and the contacting surfaces of the cylinder 1 and cylinder head 6 are sealed by the gasket 14 as the cylinder 1 and cylinder head 6 are fastened together by bolts 15.
The liquid-cooled internal combustion engine shown in FIG. 3 is similar to that shown in FIG. 1 in that it includes the cylinder 1 having the inner shell 3 and outer shell 5, the cylinder head 6 having the inner shell 8 and outer shell 10, the combustion chamber 2, its upper combustion chamber 7, cooling liquid chambers 4 and 9, the bolts 15 etc. However, in the construction shown in FIG. 3, annular grooves 16 are formed on the upper end surfaces of the inner shell 3 and outer shell 5 respectively of the cylinder 1 and have fitted therein sealing means comprising O-rings 17 formed of heat resisting rubber and having a thickness large enough to enable the rings to project outwardly from the grooves 16. The O-rings 17 are held between the end surfaces of the cylinder 1 and cylinder head 6 by the clamping force exerted by the bolts 15, to thereby provide a seal between the end surfaces.
Typical examples of the liquid-cooled internal combustion engines of the prior art have been described hereinabove. In the sealing means of the internal combustion engine shown in FIG. 1, excessive pressure is applied to the gasket 14 which undergo permanent deformation as the result of thermal expansion of the inner shells 3 and 8 and outer shells 5 and 10 as the internal combustion engine operates, so that the bolts 15 might become unable to exert enough clamping force. Also, since the area of contact between the end surfaces and the gasket 14 is large, pressure per unit area acting on the gasket 14 is low and consequently the gasket 14 is unable to perform a satisfactory sealing action, resulting in the danger that gas might leak from the combustion chamber 2. Furthermore, since the gasket 14 is pressed as the bolts 15 are tightened, the grommets 13 on the inner and outer peripheries of the asbestos plate 12 are pressed verticaly while being held and tightened. However, because of this, there is the danger that the grommets 13 might be dislodged from the boundary between them and the asbestos plate 12. Also, the asbestos plate constituting the gasket 14 is low in thermal conductivity, so that heat of combustion gas tends to collect in the stainless steel grommet 13 on the inner peripheral edge of the gasket 14 in the inner shell. As a result the grommet 13 is overheated, so that there is the danger that the fuel-air mixture in the combustion chamber might be ignited by the overheated grommet 13 and abnormal combustion of the internal combustion engine is caused to take place. Furthermore, the gasket 14 should be subjected to dipping treatment with special liquid to avoid leakage of liquid from the cooling liquid chambers and seeping of water through holes 14a for the bolts 15. Thus the production cost of the sealing means is increased.
Furthermore, in the liquid-cooled internal combustion engine shown in FIG. 3, to fit the lower end surfaces of the inner shell 8 and outer shell 10 on the upper end surfaces of the inner shell 3 and outer shell 5 respectively, it is necessary to impart high precision finishes to these end surfaces. Also, the complex shapes of the outer shells 5 and 10 which are generally the case makes it quite difficult to work them to form the annular grooves 16. In addition, to provide the annular grooves 16 in the outer shell 5 (or the outer shell 10 as the case may be) requires an increase in the thickness of the outer shells 5 and 10 or the provision of flanges 5a and 10a in the contacting portions of the outer shells 5 and 10 as shown. When the flanges 5a and 10a are provided, it is necessary to use cores for producing the cylinder 1 and cylinder head 6, thereby reducing productivity.
The following disadvantage can be cited as a serious one which is shared by the constructions shown in FIGS. 1 and 3. Generally, in this type of internal combustion engine, the pressure in the combustion chamber 2 becomes high. Thus in order to provide a satisfactory seal between the end surfaces of the inner shells 3 and 8 of the cylinder 1 and cylinder head 6 respectively, it is necessary to apply high pressure to the sealing means interposed between the inner shells 3 and 8 to positively avoid leakage of gas from the combustion chamber 2. Meanwhile the pressure in the cooling liquid chambers 4 and 9 is not as high as that in the combustion chamber 2, so that relatively low pressure has only to be applied to the sealing means arranged on the contacting surfaces of the outer shells 5 and 10. However, in conventional liquid-cooled internal combustion engines, as can be seen in FIGS. 1 and 3, the sealing means on the inner shell side and the sealing means on the outer shell side are subjected to substantially the same pressure per unit area by the bolts 15. Consequently, there might arise the situation inwhih the pressure applied to the sealing means on the inner shells 3 and 8 is not enough although unnecessarily high pressure is applied to the sealing means on the outer shells 5 and 10. Stated differently, there is the danger that the clamping force exerted by the bolts 15 is taken over by the sealing means on the outer shells 5 and 10 of larger sealing area and insufficiently high pressure is applied to the sealing means on the inner shells 3 and 8. Therefore, it is necessary to use a clamping force of very high magnitude to clamp the seaing means on the inner shell side with sufficiently high pressure as by increasing the number of the bolts 15.
This invention has as its object the provision of a liquid-cooled internal combustion engine which is free from the aforesaid disadvantages of the prior art.